Priming metal parts including brass

[DaveBaxt]

Sorry if this has been covered many times but not coming up in a search. Is the above necessary and if so how best to do this. I have used a basic metal primer but does not stick to well and is easy scratched off. Does the metal need treating prior to priming such as acetone or pickling etc?

[wefalck]

The subject has been covered indeed in several threads in recent times.

 

In a nutshell: brass forms a sort of 'greasy' oxide layer with time to which paint, incl. primer, does not adhere very well. Brass should be brightened before painting.

 

This can be done mechanically, e.g. by rubbing it with fine steel wool, using rubber-bonded fine abrasive wheels, etc. Pickling is also a solution, as discussed in a quite recent thread on pickling material, the availability will depend on your region.

 

In any case, I would wipe the pieces with acetone before painting to remove any possible traces of grease and not touch them again with bare fingers.

[DaveBaxt]

37 minutes ago, wefalck said:

The subject has been covered indeed in several threads in recent times.

 

In a nutshell: brass forms a sort of 'greasy' oxide layer with time to which paint, incl. primer, does not adhere very well. Brass should be brightened before painting.

 

This can be done mechanically, e.g. by rubbing it with fine steel wool, using rubber-bonded fine abrasive wheels, etc. Pickling is also a solution, as discussed in a quite recent thread on pickling material, the availability will depend on your region.

 

In any case, I would wipe the pieces with acetone before painting to remove any possible traces of grease and not touch them again with bare fingers.

Thank you for answering that perfectly!

[wefalck]

As an add-on: delicate parts often cannot be treated mechanically and the application of acetone might dissolve glued joints in composite parts. Brush-painting using acrylics typically is not successful, put building up thin layers of spray-paint works without de-oxidising etc.

[Roger Pellett]

If you are equipped to paint with an air bush you might want to add an “air eraser” to your tool kit.  This is an abrasive blast cleaner, about the size of an airbrush.  In addition to mechanically cleaning the surface, it adds a very fine “tooth”  to help paint adhere.  It is not so aggressive as to destroy details.

 

Here in the US we have a company called Harbor Freight that sells imported tools.  While not renown for quality, especially on this forum, I bought my air eraser there.  It was inexpensive and sturdy.  Maybe you can find a similar unit in the UK.

 

Probably not a good choice for apartment dwellers or dining room table modelers!

 

Roger

[DaveBaxt]

Unfortunately I do not own an air brush as yet .( Only modelling for a couple of years) but do have a couple of spray cans including primer. I am still currently building up my tool store but hope to one day step up and get one. The Air eraser also sounds interesting and will do a search for them and see if there available in the UK. Once again I would just like to thank every one for their help on this subject. Best regards Dave.

[Jasseji]

22 minutes ago, DaveBaxt said:

Unfortunately I do not own an air brush as yet .( Only modelling for a couple of years) but do have a couple of spray cans including primer. I am still currently building up my tool store but hope to one day step up and get one. The Air eraser also sounds interesting and will do a search for them and see if there available in the UK. Once again I would just like to thank every one for their help on this subject. Best regards Dave.

 

search Amazon, this is basically a sand blaster which looks like a regular airbrush but with a bigger container for the sand and needs a compressor to work (around 100EUR on Amazon for the compressor)

[DaveBaxt]

38 minutes ago, Jasseji said:

 

search Amazon, this is basically a sand blaster which looks like a regular airbrush but with a bigger container for the sand and needs a compressor to work (around 100EUR on Amazon for the compressor)

Thank you . Yes they look to be very reasonably priced. Best regards Dave

Edited September 22, 2021 by DaveBaxt

[wefalck]

As Roger said, when contemplating on of these air-erasers, one has to carefully consider the modelling environment. They were developed originally for professional draughtspeople, so a sandblasting-booth is not necessarily needed, but the resulting dust would not be welcome in a domestic environment. There are, however, also shoebox-sized sandblasting boxes that are sold together with them. Railway modellers seem to use them quite frequently to prepare their etched-brass kits for painting.

 

When buying a compressor to use in a domestic environment, particularly in an appartment, the noise and vibration generated can also be an issue. Cheap models may be a problem in this context. Also, an air-eraser needs more pressure to be effective, than an air-brush.

[DaveBaxt]

Ah! rhat 

7 hours ago, wefalck said:

As Roger said, when contemplating on of these air-erasers, one has to carefully consider the modelling environment. They were developed originally for professional draughtspeople, so a sandblasting-booth is not necessarily needed, but the resulting dust would not be welcome in a domestic environment. There are, however, also shoebox-sized sandblasting boxes that are sold together with them. Railway modellers seem to use them quite frequently to prepare their etched-brass kits for painting.

 

When buying a compressor to use in a domestic environment, particularly in an appartment, the noise and vibration generated can also be an issue. Cheap models may be a problem in this context. Also, an air-eraser needs more pressure to be effective, than an air-brush.

Ah! that was the question I was asking myself ( but as usual I didn't know the answer) So \if I decided to go down the air brush route for painting I would need another compressor or can you raise the pressure enough to work for both? I have just received my crock pot  and Sparex for pickling so for the time being I will be using this for removing any unwanted residues, but always nice to lean about more alternatives. Thank you once again for your input. Best regards Dave

[Jasseji]

Just now, DaveBaxt said:

Ah! rhat 

Ah! that was the question I was asking myself ( but as usual I didn't know the answer) So \if I decided to go down the air brush route for painting I would need another compressor or can you raise the pressure enough to work for both? I have just received my crock pot  and Sparex for pickling so for the time being I will be using this for removing any unwanted residues, but always nice to lean about more alternatives. Thank you once again for your input. Best regards Dave

 

The Air Erasers require 2.5-4.5 bar pressure, a standard Single-Piston Airbrush Compressor goes up to 4 bar (the stable range is 3-3.5bar).

 

To be on the safe side you'd need ideally a Double-Piston Compressor which are only slightly more expensive (20-30 euro more than a single-piston) and they go up to 6-7bar

[DaveBaxt]

1 hour ago, Jasseji said:

 

The Air Erasers require 2.5-4.5 bar pressure, a standard Single-Piston Airbrush Compressor goes up to 4 bar (the stable range is 3-3.5bar).

 

To be on the safe side you'd need ideally a Double-Piston Compressor which are only slightly more expensive (20-30 euro more than a single-piston) and they go up to 6-7bar

I am assuming its just a case of adjusting a pressure switch to get the required output pressure or is it more complicated than that?

[Jasseji]

16 minutes ago, DaveBaxt said:

I am assuming its just a case of adjusting a pressure switch to get the required output pressure or is it more complicated than that?

It's a valve where you can Set the pressure and there is a dual to Show what pressure is bei g deliverrd 

[Roger Pellett]

My compressor that cost about $100 US has a top pressure of about 8 BAR (125 psi).  It also has a tank and a built in pressure regulator that allows output pressure to be turned down as needed.  These compressors are sold by large home improvement stores throughout the US.  It’s noisy, but so are my other full sized power tools.  My wife has been putting up with noise and dirt from an in home workshop for over 50 years.  My first workshop was the second bedroom of a two bedroom Apartment.  When you need a tool, buy the right one and it will last you a lifetime.

 

Roger

[wefalck]

A tank is a must for a useful compressor - otherwise you will have constant pressure fluctuations.

[Jasseji]

38 minutes ago, Roger Pellett said:

My compressor that cost about $100 US has a top pressure of about 8 BAR (125 psi).  It also has a tank and a built in pressure regulator that allows output pressure to be turned down as needed.  These compressors are sold by large home improvement stores throughout the US.  It’s noisy, but so are my other full sized power tools.  My wife has been putting up with noise and dirt from an in home workshop for over 50 years.  My first workshop was the second bedroom of a two bedroom Apartment.  When you need a tool, buy the right one and it will last you a lifetime.

 

Roger

Oh, then you  have bettercompressors over there in the US, the ones for ~100€ over here run max at 6 Bars (but they are quiet on the other hand)